[eesmith]

Why would it be cool?

We can do something like that already with current flowing in a circle in a superconductor. Resistance corresponds to friction. In the worst case you get a quench and all of the stored angular momentum results in a torque that breaks your machine.

[beautifulfreak]

Because it would do work in a novel way. It could be used to levitate a spaceship, for example.

[eesmith]

No, it wouldn't. It would cause a torque as the momentum from the fluid is transferred to the torus. It would not cause a lift. There's no overall momentum change.

It's basically a gyroscope, albeit with quantized vorticies.

An external magnetic field could be used to levitate an object. But that's not novel.